1. Field of the Invention
This invention relates to radio frequency devices of the type comprising a signal processing means joined to electromagnetic transmission means, which in operation are latently susceptible to electromagnetic interference (EMI) and/or radio frequency leakage.
2. Description of the Related Art
In the use of radio frequency (RF) devices, such as for example impedance matching or coupling devices, ground protection devices (ground fault interrupter systems), radar transmitters and/or receivers, and signal splitters, it is well established that EMI and RF leakage into or out of the device seriously adversely affect its operation.
Accordingly, various means have been developed for shielding such devices from electromagnetic or radio frequency interference, e.g., plate member and housings constructed of materials which absorb radio and other electromagnetic waves.
Such shielding elements are generally useful in attenuating EMI/RF interference in the signal processing portion of the device, but do not solve the problem of EMI or RF leakage associated with the junction of this portion and the external leads, e.g., electrical cables or wires, which transmit electromagnetic signals into or out of the signal processing portion.
In some systems, it is conventional practice to utilize "rubber boots" over the couplings joining the signal processing unit and its external leads to eliminate or reduce to a suitably low level the effects of EMI and RF leakage at such couplings. These boots, which are similar in design to the covers used in automotive systems for spark plug connector wires, generally work well initially if properly fitted to cover the associted coupling.
However, the rubber boots, due to the generally high coefficient of friction on the interior surfaces mating with the coupling, frequently tend to be poorly installed, so that they incompletely cover the coupling, and allow EMI and RF leakage to adversely affect the operation of the device.
In systems which are subject in use to vibration, translation, flexural stresses on the leads and/or signal processing unit, etc., the couplings, even if overlaid with rubber boots, tend to loosen, and thereby increase the susceptibility of the system to EMI and RF leakage.
In addition to the foregoing problems, where the RF device is employed in an exterior environment, corrosion of the coupling and associated elements of the device may occur due to atmospheric moisture. Such corrosion may be accelerated by the presence of dissimilar metals in the couplings or adjacent portions of the device, with consequent adverse effect on the structural integrity as well as the performance characteristics of the device.
Poorly fitted, or loosened boots, facilitate the corrosive action. Although it is known to coat the couplings, and the interior surfaces of boots employed thereover, with silicone greases to serve as moisture permeation barriers, such greases dry out and crack or otherwise dissipate in use, so that their anti-corrosion action is lost.
The foregoing problems are especially severe in the case of cable television junction boxes, which are typically employed in exterior environments on overhead or underground signal cables, and have a plurality of couplings joining the box to the signal cable and the service (output) cables. In such environments, the junction box/cable couplings readily tend to work loose, as well as corrode.
Accordingly, it would be a significant advance in the art to provide an improved means for reducing or eliminating EMI as well as RF leakage, at the junction of signal processing means and electromagnetic transmission means (external leads) in RF devices of the type described above, such means preferably providing corrosion protection at such junction.
It is therefore an object of the present invention to provide such an improved means which is readily deployed, simple and economical in character, and adapted in application to existing, as well as contemporaneously fabricated, RF devices.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.